Method of making relief printing plate matrices and article



E. W. FUERST ET AL May 18 1954 METHOD OF MAKING RELIEF PRINTING PLATEMATRICES AND ARTICLE Filed March 20, 19 52 R E T S A M 5 u 0 R o PASPHALT SEALING COA okous MASTER 1 E. El.

SENSITIVE LAYER SEAL NG C AT \7 EXPOSURE a oavsm mam POROUS MASTER f H 2M M 60 0 N NU 1 mW[ W MM &W M M w W I c u S Patented May 18, 1954 METHODOF MAKING RELIEF PRINTING PLATE MATRICES AND ARTICLE Edwin W. Fuerst andWilliam F. Fuerst, Toledo, Ohio, assignors to The Printing Die Company,Toledo, Ohio, a corporation of Ohio Application March 20, 1952, SerialNo. 277,602

Claims.

This invention relates to the art of relief printing.

In one aspect, this invention consists in a new and improved method forphotomechanically making masters for printing plates in an efiicient andeconomical manner, greatly reducing the time and cost herebeforerequired for this purpose. It is particularly advantageous in theproduction of printing plates in which the relief pattern is of quiteconsiderable depth and where greater fidelity than has heretofore beenpossible is of importance. The well-known acid etching process, as wellas attempts in this direction from the use of sandblasting, have notresulted in achieving the desired depth of out. One major difficulty hasresided in the undercutting of the pattern when effort has been toproduce a design of an unusual depth. This difii culty is obviatedaccording to this invention, and a commercially satisfactory method isproduced by which rubber printing matrices, for example, can be made ina practical, efiicient and economical manner so that a faithful andsharp reproduction results, in which the relief is much deeper thancould heretofore be produced, so far as we are aware.

An object is to produce a new and improved method of photomechanicallymaking a self-sustaining master in which the relief image is formedunusually deep without objectionable undercutting and from which amatrix may be formed.

Another object is to produce a novel method of producing printing platematrices involving the use of a porous bat or master, forming a reliefimage thereon photomechanically, and finally casting die metal on themaster while the porous master is subjected to subatmospheric pressure.A further object is to produce an improved method of etching bysandblasting in such manner that not only may the relief image beunusually deep, but uniformly sharp and accurate. Other objects andadvantages will hereinafter appear, and for purposes of illustration butnot of limitation, an embodiment of the invention is shown on theaccompanying drawings, in which Figure 1 is a perspective View of aporous master or bat from which the printing plate matrix is formed;

Figure 2 is a fragmentary sectional view showing the porous master withits upper face or surface coated with a sealing layer;

Figure 3 is a fragmentary sectional view show ing a succeeding step inwhich the master having a sealing coat, is successively coated with anasphaltic and a light-sensitive layer;

, Figure 4 is a fragmentary sectional view showing the next succeedingstep in which the lightsensitive layer is exposed and developed and theundeveloped portions removed to form the stencil;

Figure 5 is a fragmentary View partly in section showing the action ofthe sandblasting; and

Figure 6 is a sectional view showing the manner in which the master isutilized in the casting of the matrix and with the porous mastersubjected to suction or subatmospheric pressure.

In accordance with this invention, the first step is to produce a bat ormaster of porous material, such as indicated at It on the drawings. Onesatisfactory material is made from plaster of Paris and water, themixture being cast on plate glass so that the surface is entirely flatand smooth. After the bat is cast, it must be thoroughly and properlydried in order to achieve uniform hardness throughout. The size of thebat may be varied in accordance with the size and shape of the printingdie to be produced. After the plaster bat has been properly dried, asealing coat H is applied to the flat surface, i. e. that surface whichhas been in contact with the plate glass and which, as indicated, isentirely smooth and fiat. As will hereinafter appear,

an asphalt layer or resist is applied to the sealing coat and the sealincoat must be such as to prevent any penetration of the asphalt coat intothe plaster bat. Furthermore, the sealing coat must not penetrate theplaster bat itself. Furthermore, the sealing coat must be softer thanthe plaster bat in order to provide less resistance than the bat to theaction of sandblasting. An exceedingly satisfactory material for thesealing coat is a mixture of starch containing about fifteen percent byweight of glycerin, the starch being first cooked on the slow fire untilit jells and thereafter the glycerin being added while hot. Glycerin isfound to be desirable since it has a greater affinity for water thandoes starch and it serves to militate against the plaster bat inabsorbing the water from the starch. After the mixture has beenprepared, the sealing coat is applied to the flat surface of the plasterbat or master and is allowed to air dry for approximately two days.

Another material which has been found satisfactory for use as a sealingcoat is a wax emulsion containing the same proportion of glycerin asabove mentioned.

After the sealing coat is properly dried, a relatively thin asphalt coati2 is sprayed upon the sealing coat. The asphalt coat must have acontrolled hardness and to achieve this result, asphalt and Gilsoniteare mixed together, a suitable composition consisting of half of each ofthese ingredients. Upon the asphalt coat is applied a layer It oflight-sensitive material. We have found that bichromated lue andbichromated gelatin containing a rubber latex is satisfactory for thispurpose, but since this material per se forms no part of the presentinvention, de tail description of same is not considered necessary, itbeing regarded as sufficient to make reference to the United StatesPatent to Staehle,

No. 2,533,530, dated December 12, 1950.

The light-sensitive layer is exposed to light and a relief image isconsequently formed in the sensitive layer, soluble portions of thegelatin being washed away to produce the desired stencil as indicated onFigure 4.

In the next step, the master is subjected to etching by sandblasting andfor this purpose, a relatively long nozzle it is employed which isrelatively movable with respect to the master it. It is found thatsatisfactory results can be accomplished by forcing the sand through thenozzle under an air pressure of approximately six pounds per square inchwhen employing a inch' nozzle. The depth of the cut in the master may becontrolled either by varying the blasting pressure or the time duringwhich the master is subjected to the blast. The purpose of a relativelylong nozzle is to straighten the trajectory of the grains of sand sothat they against the master in an almost straight vertical fashion. Therelatively low air pressure employed is to prevent undesired fanning ofthe stream issuing from the nozzle Hi, and thereby militate againstundercutting. Figure 5 diagrammatically illustrates the action of thesandblast as above described. The sand is blasted through the severallayers as definedby the stencil and when directly over the area to beblasted, it wears away a groove or cavity, the side walls of which areslightly tapered. However, as the relative movement occurs between thenozzle it and the master Hi, the slight fanning which occurs in thestream and which is of less intensity, not only straightens out thesides of the cut, but also effects a deeper cut.

One important feature resides in controlling the degree of hardness ofthe several layers and the master. in the situation, the resistance tothe sandblast should range from the plaster master as the greatest, tothe asphalt as the least. It is most ii lportant that the plaster shouldbe the most resistant of these layers, it being manifest that thesandblast should pass readily through the asphalt layer as well as thesealing coat. In this manner, an unusually deep relief image may beproduced with exceedingly sharp and accurate pattern. This unusual depthis of particular importance in the ultimate production of a rubberprinting plate, as will be readily recognized by those skilled in thisart.

After the sandblasting, the several layers are removed, as for exampleby immersion in hot water. In this connection, since the starch sealingcoat is quickly removed by hot water, the superposed asphalt coat ismore readily removed.

Thereafter, the master bat ill with the relief image sandblasted on theflat surface thereof, is placed in a receptacle l5 and upon the uppersurface of the master is placed a cope it which is also of porousplaster of Paris. Molten metal is poured from a ladle L into a sprue ll,substantially filling the s'prue and at the same time, the under side ofthe master it is subjected to subatmospheric pressure or suction throughthe tube 4 H3. In view of the porosity of the master and cope, themaster cavity is evacuated, and this not only produces a printing platematrix which is homogeneous throughout, but also facilitates the castingoperation.

It is to be understood'that numerous changes in details of construction,arrangement, operation and choice of materials may be effected withoutdeparting from the spirit of the invention especiallyas defined in theappended claims.

What we claim is: r

1. An article for use in the production of relief printing plates,comprising; a master of air pervious, friable material; a sealing coaton the master, an undercoat of asphalt on the sealing coat, and a layerof light-sensitive material on the undercoat, whereby a relief image maybe formed in master by exposure of the layer to light, washing awayunhardened portions thereof and removing the coat, layer and apertion ofthe master by sandblasting through those parts of the layer whereportions thereof have been removed.

2. The combination claimed in claim 1, said sealing coat being lessresistant to eandblast than said master, and said asphalt layer beingless resistant to sandblast than the sealing coat.

3. The method of making masters for use in the production of reliefprinting plates which producing a master of air pervious. friablematerial, coating the surface of the master successively with a sealingcoat, an underccat of asphalt and a layer of light-sensitive materialcontaining rubber latex, forming a relief image in said layer byexposure to light and washing away unhardened portions thereof, andremoving the coat, undercoat, layer and a portion of the master bysandblasting in those parts of the layer where portions thereof havebeen removed with a. stream perpendicular to the master under pressurewhich is equivalent to that of approximately six pounds per square inchwhen employing a {*5 inch nozzle.

4. The method of making matrices for relief printing plates whichconsists in producing a porous master having a relief image sandblastedtherein, casting the printing plate matrix, and concomitantly with thecasting step, evacuating the master through the porous structure thereof5. The method of making a matrix for relief printing plates whichconsists in producing a master of air pervious friable material, coatingthe surface of the master successively with a sealing coat, an undercoatof asphalt and a layer of light-sensitive material containingbiohromated gelatin, glue and rubber latex, forming a relief image insaid layer by exposure to light, removing unhardened portions of thelight-sensitive material by immersion in a solvent, sand blastingthrough those part of the layer where portions thereof have been removedthereby to form the relief image in the master, removing the coat,undercoat and layer, casting the printing plate matrix on the master,and concomitantly with the casting step evacuating the master byapplying suction to the reverse side thereof.

References Cited in the file of this patent UNITED STATES PATENTS

1. AN ARTICLE FOR USE IN THE PRODUCTION OF RELIEF PRINTING PLATES,COMPRISING ; A MASTER OF AIRPERVIOUS, FRIABLE MATERIAL; A SEALING COATON THE MASTER, AN UNDERCOAT OF ASPHALT ON THE SEALING COAT, AND A LAYEROF LIGHT-SENSITIVE MATERIAL ON THE UNDERCOAT, WHEREBY A RELIEF IMAGE MAYBE FORMED IN SAID MASTER BY EXPOSURE OF THE LAYER TO LIGHT, WASHING AWAYUNHARDENED PORTIONS THEREOF AND REMOVING THE COAT, LAYER AND A PORTIONOF THE MASTER BY SANDBLASTING THROUGH THOSE PARTS OF THE LAYER WHEREPORTIONS THEREOF HAVE BEEN REMOVED.